The present invention relates to a power tool for surface treatment.
More particularly, it relates to a power tool with a housing, a motor arranged in the housing, and a rotary, circulatory or swinging tool driven by the motor and having a triangular base surface for receiving a triangular grinding sheet.
Power tools of the above mentioned general type are known in the art. One of such power tools is disclosed for example in U.S. Pat. No. 3,160,995. The power tool disclosed in this reference is used for grinding of surfaces near their edges, in particular in corners or along grooves. The power tool has a grinding disc with a triangular base surface. Its working movement is performed reciprocatingly in a swinging manner around a stationary axis extending perpendicular to the base surface. The axis of the grinding disc extends geometrically close to a corner which faces forwardly. The angle of the corner in the front region of the grinding disc is smaller than 90.degree., and therefore the grinding disc can be used up to the outermost, edge-adjacent region of corners or grooves for grinding. In such a power tool which is further developed and has the axis extending centrally geometrically through the grinding disc, the edges of the grinding tool are curved, which is also known as flatiron, for grinding at locations which are difficult to access and flush with the edges.
The contour of the grinding disc which is formed as a unilateral triangle, similar to flatiron with curved side edges, has three corner angles, similarly to all such triangles, which corner angles are smaller than 90.degree..
Furthermore, power tools with rectangular grinding discs are known which are provided with an eccentric drive for performing a fixed circulatory movement. These power tools are identified as swinging discs, despite the fact that their tool does not perform a swinging movement in its exact meaning.
A further development of the swinging discs led to eccentric grinders with unfixed, circulatory and rotary grinding disc. Its movement is controllable by adjusting of several, different operational stages.
The known power tools are power-efficient, however they have relatively expensive constructions. They also have a high weight, a high energy consumption, a high noise generation and require auxiliary tools for their tool exchange, for example to exchange the grinding discs.